One method to operate an internal combustion engine having a turbocharger is presented in U.S. Pat. No. 6,202,414. This method presents a way to balance the output of two turbochargers that are in communication with different cylinder banks of a “V” engine. Balancing the output of two turbochargers can improve turbocharger efficiency and mitigate the possibility of compressor surge. This method uses, state parameters that are in the vicinity of the turbocharger compressors to adjust the effective turbine cross section, thereby regulating compressor flow. The method attempts to reduce any difference in state parameters between two cylinder groups to zero. That is, the method attempts to equalize the state parameters of the two cylinder groups that are in communication with the two turbochargers.
The above-mentioned method can also have several disadvantages. For example, the method simply adjusts a turbocharger waste gate or variable geometry vane position, thereby simultaneously affecting turbocharger and cylinder operation. Specifically, turbine energy is altered along with the amount of air and exhaust gas residuals that comprise the cylinder mixture. In other words, adjusting the waste gate or vane position changes the exhaust backpressure and can affect the amount of exhaust gas residuals that are trapped in a cylinder since the exhaust backpressure acts to impede flow from the cylinder. Further, when cylinder volume is displaced by additional residual exhaust gas, there is less available space for fresh air in the cylinder. Consequently, cylinder charge air amount and cylinder charge residual amount may change in an undesirable manner when a waste gate or turbine vanes are adjusted to regulate a turbocharger. As a result, regulation and/or control of a turbocharger may have undesirable effects on engine emissions, fuel consumption, performance, audible noise, and uniform cylinder torque production.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method to control an engine having variable event valve operation and at least one turbocharger.